docs: def checkmagic(self):
          """
          Overridable.
          Check to see if the file object self.lib actually has a file
          we understand.
          """
          self.lib.seek(self.start)  # default - magic is at start of file
  
          if self.lib.read(len(self.MAGIC)) != self.MAGIC:
              raise ArchiveReadError("%s is not a valid %s archive file"
                                     % (self.path, self.__class__.__name__))
  
          if self.lib.read(len(self.pymagic)) != self.pymagic:
              raise ArchiveReadError("%s has version mismatch to dll" %
                  (self.path))
  
          self.lib.read(4)